This invention relates to a method of fabricating a semiconductor device such as a complementary metal-oxide semiconductor large-scale integrated circuit (CMOSLSI) or an integrated circuit including field-effect transistors.
CMOSLSIs are widely used since they consume small rates of electric power. Recently, the hot carrier effect has caused a serious problem in developing large-scale integrated circuits (LSIs).
The hot carrier effect results for the following reason. While the sizes of metal-oxide semiconductor (MOS) devices have been decreased, the power supply voltage applied to them has been fixed at 5 volts. Specifically, in a small-size MOS device, the applied power supply voltage induces a high electric field which releases some electrons from bound states. When the electrons are released, hot carriers having high energies are generated. Such hot carriers tend to be trapped within a gate oxide film of the MOS device. The trapped carriers deteriorate the characteristics of the MOS device.
The lightly doped drain (LDD) structure is a known countermeasure against the hot carrier effect. As will be explained later, a prior art method of fabricating a semiconductor device using an LDD structure has another problem lowering the characteristics of the semiconductor device.